1. Field of the Invention
The present invention relates to an ignition apparatus for internal combustion engines.
2. Description of the Prior Art
The ignition apparatus of a conventional internal combustion engine is constructed as shown in FIG. 1 or 2 so that a current supplied from a battery 1 having one of its terminals grounded flows to ground through a primary winding 3a of an ignition coil 3 and a breaker 2. A high voltage induced in the ignition coil 3 is delivered from one end (FIG. 1) or respective ends (FIG. 2) of a secondary winding 3b and applied to a terminal or terminals of a spark plug or spark plugs 4, respectively. Also, a conventional spark plug 4 is constructed as shown in FIG. 3 so that a terminal a and a center electrode f are fixed to each other with an electrically conductive glass seal g to provide electrical conduction therebetween, while, they are also electrically insulated from a metallic shell d by an insulator b. The metallic shell d has a mounting screw for mounting the plug on the engine and it is adapted to be tightly screwed into a cylinder head of the engine with a gasket k intervening therebetween. A ground electrode e is attached to an end surface of the metallic shell d by welding or the like and thus it has electrical conduction with the cylinder head. Formed between the center electrode f and the ground electrode e is a spark gap h for causing spark discharge therethrough.
The operation of this prior art apparatus is such that a high voltage supplied from the secondary winding 3b of the ignition coil 3 is applied to the center electrode f through the terminal a of the spark plug 4 and spark discharge occurs through the spark gap h as the applied voltage exceeds the sparking voltage of the spark gap h thereby igniting a mixture gas.
Recently, there has been a strong demand for the improvement of various performances of the spark plug itself, e.g., the promotion of ignition performance, the improved resistance to fouling and the reduced radio frequency interference. However, there is a limit in satisfying these requirements sufficiently only through modifications of the construction of the spark plug itself.